JP2010131810A - Biaxially stretched multilayered polyamide resin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially stretched multilayered polyamide resin film reduced in change in dynamic characteristics caused by a humidity change by stretching a polyamide resin film in which a lamellar compound represented by a lamellar silicate or the like heretofore considered to be difficult to be stretched is uniformly dispersed. <P>SOLUTION: The biaxially stretched multilayered polyamide resin film is obtained by stretching the polyamide resin film to which 0.3-20 wt.% of an inorganic substance containing a lamellar compound is added and which is composed of eight layers or more, 2.5-5.0 times in its longitudinal direction and 3.0-6.0 times in its width direction and characterized in that the ratio of the product (X1) of the maximum point stress (MPa) and the elongation at break (%) of a sample which has an equilibrium water absorption of 3.0-7.0% and is kept at a relative humidity of 40% for 12 hours, calculated under a condition of the relative humidity of 40%, an original length of 40 mm, a width of 10 mm and a deformation speed of 200 mm/min according to JIS K 7113 and the product (X2) of the maximum point stress (MPa) and the elongation at break (%) of the sample preserved at a relative humidity of 80% for 12 hours is 1.0-1.5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention generally relates to a film made of a resin containing a layered compound called a nanocomposite. More specifically, the present invention relates to a stretched film of a nanocomposite polyamide resin, which has been conventionally said to be impossible to stretch at a high magnification with an addition amount of 1% or more. Conventional nylon films have large changes in properties due to changes in humidity, but films using inorganic layered compounds have little change in mechanical properties due to changes in humidity, and the present invention provides polyamide films with excellent processability. It can be used for packaging materials.

  Biaxially stretched polyamide resin films are excellent in mechanical properties, barrier properties, pinhole resistance, transparency and the like, and are widely used as packaging materials. However, due to the high hygroscopic property derived from the amide bond in the resin skeleton, the mechanical strength changes due to the change in humidity, and hygroscopic elongation occurs, and problems are likely to occur in various processes. For example, a polyamide film made of ordinary nylon 6 has a high modulus of elasticity under low humidity but a low elongation, and the maximum point stress is correspondingly small. Under humidity, the elastic modulus is small, but the elongation is large, and the maximum point stress is correspondingly large, which indicates ductility. Under stretching conditions that improve the characteristics on the low humidity side, problems such as the film characteristics being unbalanced occur. As described above, characteristics of a normal polyamide film greatly change depending on humidity as compared with a film made of polyethylene terephthalate. For this reason, it is necessary to control the humidity in the processing, or to determine the processing conditions in advance in consideration of a change in characteristics.

  As a method for improving heat resistance and hygroscopicity of polyamide resin, it is known to uniformly disperse layered silicate, and this method is known as nanocomposite formation. Since various properties described above are improved by nanocompositing, it is expected that a film with improved properties will be obtained by filming, but in reality, these resins are generally poor in stretchability, It is not suitable as a resin for stretched films. In particular, it is said that it is necessary to add 1% or more of a layered silicate to a polyamide resin in order to sufficiently enhance the effect of improving the mechanical properties, but a polyamide resin having such a high layered silicate content. Then, the difficulty of stretching was remarkable.

Patent Document 1 discloses a biaxially stretched polyamide film containing a layered silicate, but in order to overcome the difficulty of stretching, the maximum temperature reached 180 ° by successive stretching in the width direction next to the length direction. A high temperature of −200 ° C. is essential, and the layered silicate is not sufficiently oriented because the crystal proceeds excessively before sufficient stretching in the width direction is achieved, as well as difficulty in production. In other words, there are problems that the effect of adding various layered silicates does not appear, thickness spots occur in fine regions, and pinhole resistance is not achieved.
JP 2003-20349 A

  Furthermore, even if such a special method is adopted, as can be seen from the claims, it is practically 1% by weight or less (including the organic component contained between the layers), and beyond that, whitening during stretching, It has been pointed out that the productivity is poor at high stretch ratios. This is considered to be because stress tends to concentrate on the tip of the layered compound during stretching, and glazes and cracks are likely to occur.

Patent Document 2 also discloses a patent for a stretched film in which a layered inorganic compound is added in an amount of 0.5 to 5%, but there is no specific measure for solving the above-described poor stretchability. There is no description, and it is the result of examination at the level where small pieces were simultaneously biaxially stretched in the laboratory, industrial production by sequential biaxial stretching in a system to which a layered compound at a high concentration of 1% or more was added There is no technical disclosure about the stretching method having the property. In addition, there is a description in the text that layered inorganic compounds such as montmorillonite are effective in improving slipperiness by blocking water absorption, but when a material such as montmorillonite is added to nylon resin, the equilibrium water absorption rate of the resin is To increase. From this, it can be said that the essence of the invention largely depends on the effect of addition of the inorganic lubricant.
JP 2003-313322 A

  As described above, industrial production of a stretched film made of a polyamide resin excellent in the above-described various properties has been difficult on the extension lines of the prior art.

  The present invention makes it possible to stretch a polyamide resin film in which a layered compound typified by layered silicate, which has been conventionally difficult to stretch, is uniformly dispersed, and is a biaxially stretched polyamide with little change in mechanical properties due to changes in humidity. It is an object to provide a resin film.

The inventor has studied the stretching of a polyamide resin containing a layered compound for the purpose of improving the maximum point stress particularly under low humidity, and has reached the present invention. That is, this invention consists of the following structures.
1. A biaxially stretched polyamide resin film obtained by adding 0.3 to 20% by weight of an inorganic substance containing a layered compound, laminated in 8 or more layers, and stretched 2.5 to 5.0 times in the longitudinal direction and 3.0 to 6.0 times in the width direction. 12 hours at a humidity of 40% required by the method described in JIS K 7113 under the conditions of an equilibrium water absorption of 3.0 to 7.0% and an original length of 40 mm, a width of 10 mm and a deformation rate of 200 mm / min stored at a relative humidity of 40%. The product of the maximum point stress (MPa) and the breaking elongation (%) of the stored sample (X1), and the maximum point stress (MPa) and the breaking elongation (%) of the sample stored for 12 hours at 80% relative humidity A biaxially stretched polyamide resin film, wherein the product (X2) ratio is in the range of 1.0 to 1.5.

  According to the present invention, it is possible to provide a polyamide resin film with little change in strength of the film due to humidity and excellent in other characteristics.

The present invention is described in detail below.
(Polyamide resin)
The polyamide resin used in the present invention is not particularly limited, such as a ring-opening polymer of a cyclic lactam, a condensate of diamine and dicarboxylic acid, and a self-condensate of amino acids. For example, nylon 6, nylon 7, nylon 66, Examples include, but are not limited to, nylon 11, nylon 12, nylon 4, nylon 46, nylon 69, nylon 612, and metaxylylenediamine-based nylon. It is also possible to use a copolymerized polyamide resin. Specifically, nylon 6 and nylon 66 copolymerized with metaxylylenediamine, nylon 6T, nylon 6I, nylon 6 / 6T copolymer, nylon 6 / 6I copolymer, nylon 6 / polyalkylene glycol resin, nylon 11 / Polyalkylene glycol resin, nylon 12 / polyalkylene glycol resin, nylon 6 / MXD6 copolymer and other aromatic polyamide resins can be used, but other components copolymerized can also be used, preferably nylon 6, nylon 66, and metaxylylenediamine-based nylon are preferable. In particular, gas permeability can be greatly reduced by laminating a small amount of a layer made of metaxylylenediamine-based nylon resin, which is one of the preferred examples in the present invention.

  In addition to the polyamide resin described later, other resins and additives may be added to these resins. Moreover, it is one of preferable embodiments that the collection film manufactured by this patent is used as a part or all of the polyamide resin from the economical aspect. As other resins, known resins such as a polyester resin, a polyurethane resin, an acrylic resin, a polycarbonate resin, a polyolefin resin, a polyester elastomer resin, and a polyamide elastomer resin can be used, but are not limited thereto. In addition, in terms of slipperiness, various lubricants can be added for the purpose of imparting surface roughness, and both organic lubricants and inorganic lubricants can be used. Although not limited, in the present invention, it is preferable that sufficient slipperiness can be imparted without the addition of these lubricants, and the type and amount of lubricant to be added should be determined in consideration of various characteristics. In the case of an inorganic lubricant, the particle diameter is preferably 0.5 μm or more, more preferably 1 μm or more. The addition amount is preferably in the range of 100 to 5000 ppm in the layer forming the surface layer. If it is 100 ppm or less, the effect of addition is small, and if it exceeds 5000 ppm, the effect is saturated, so it is not economical.

(Polyamide resin in which layered compound is uniformly dispersed)
In the present invention, the polyamide resin in which the layered compound is uniformly dispersed is generally called nanocomposite nylon. It is preferable that the layered compound is uniformly dispersed and does not contain a coarse material having a thickness of the layered compound exceeding 2 μm. Including a coarse product exceeding 2 μm is not preferable because transparency and stretchability are reduced.

  Examples of the layered compound include layered compounds such as swellable mica, clay, montmorillonite, smectite, and hydrotalcite, but are not limited to these and can be used regardless of inorganic or organic. The shape of the layered compound is not particularly limited, but the average length of the major axis is 0.01 to 50 μm, preferably 0.03 to 20 μm, particularly preferably 0.05 to 12 μm, and the aspect ratio is 5 to 5000. Preferably, those having 10 to 5000 can be suitably used. The amount of the inorganic layered compound added to the polyamide resin is preferably 0.3 to 20% by weight. The inorganic layered compound may be added as an organically treated layered compound, and the amount added may not always match the content of inorganic substances (added amount) due to the weight residue described below. In addition, if a method for obtaining from a weight residue as described later is employed, a small amount of an inorganic substance other than the layered inorganic compound may be added in addition, and in the present invention, it is obtained as an added amount of the inorganic substance containing the layered compound. become. In the present invention, the amount of the inorganic substance containing the layered compound is a value obtained by subtracting the ash from the weight residue obtained by the calorimeter (TGA). Specifically, the temperature increases from room temperature to 500 ° C. of the resin containing the layered compound. Obtained weight residue after warming, and then obtained by subtracting the value of resin ash. In the case of Example 1, the inorganic content was 2.6% by subtracting 4.4% weight residue by TGA and 1.8% weight residue from resin. Can be sought. Further, the ratio of the organic treating agent in the layered compound can be obtained separately by TGA and calculated from the numerical value.

  The lower limit value of the layered compound content is more preferably 0.3% or more, further preferably 0.5% or more, and most preferably 0.7% or more. If it is less than 0.3%, it is small in terms of dimensional stability and mechanical properties, and therefore the effect of adding a layered compound is small and not preferable. In addition, the coefficient of static friction increases and slipperiness may decrease.

The upper limit is more preferably 15% or less, still more preferably 10% or less. If it exceeds 20%, the effect of reducing the humidity dependency is saturated, which is not economical, and the fluidity at the time of melting is also lowered. In addition, the surface roughness becomes unnecessarily large or haze decreases.
Although these layered compounds can be used in general, commercially available organically treated products that are suitably used in the monomer insertion polymerization method described below include Cloisite from Southern Clay Products, Somasif and Lucentite from Corp Chemical, Examples include Hosoon Sben.

In the present invention, it is preferable that the layered compound is uniformly dispersed in the above-described polyamide resin.
1) Interlayer insertion method:
1) Monomer insertion polymerization method 2) Polymer insertion method 3) Organic low molecular insertion (organic swelling) kneading method 2) In-situ method: In-situ filler formation method (sol-gel method)
3) Ultrafine particle direct dispersion method and the like. Examples of commercially available materials include Cress Alon NF3040 and NF3020 manufactured by Nanopolymer Composite Corp., NCH 1015C2 manufactured by Ube Industries, Imperm103 and Imperm105 manufactured by Nanocor, and the like. The layered compound is preferably treated with various organic treating agents for the purpose of enhancing the dispersibility of the layered compound in order to suppress the generation of coarse compounds of the layered compound contained in the polyamide resin. In order to avoid adverse effects due to thermal decomposition of the treatment agent, those obtained by using a low molecular weight compound having good thermal stability or a monomer insertion polymerization method without using a low molecular weight compound are preferred. Regarding thermal stability, a compound having a 5% weight loss temperature of 150 ° C. or higher of the treated layered compound is preferable. TGA etc. can be used for the measurement. Low thermal stability is undesirable because it may cause bubbles in the film or cause coloration (challenge nanotech materials, polymer nanocomposites with widespread use, published by Sumibe Tsutsunaka Techno Co., Ltd.) See).

  These layered compounds are preferably oriented in the plane of the obtained film in order to develop the characteristics. The in-plane orientation can be confirmed by observing the cross section using a transmission electron microscope or a scanning electron microscope.

(Film forming method)
In the stretching of the resin containing a layered compound in the present invention, the problems in stretching using sequential biaxial stretching, which is generally advantageous in terms of economy, are as follows: (1) Longitudinal direction (hereinafter abbreviated as MD) During stretching, crystallization proceeds with heat during stretching, and the stretchability in the transverse direction (hereinafter abbreviated as TD) is lost after uniaxial stretching. (2) Breakage occurs during TD stretching. (3) After TD stretching The following three points are included: rupture occurs during heat setting of (1). Regarding (1), MD stretching conditions that allow TD stretching and MD stretching conditions that do not allow TD stretching are arranged. It was found that there was a difference in the refractive index in the width direction of the sheet (refractive index in the Y-axis direction, hereinafter abbreviated as Ny). Specifically, Ny of a uniaxially stretched sheet that can be TD-stretched is Ny smaller after MD stretching, whereas TD stretching cannot be performed (that is, whitening or breaking occurs during TD stretching) Ny showed little or no change in Ny after MD stretching. In normal polyamide resin stretching, Ny after MD stretching causes necking in the width direction during MD stretching and Ny decreases at the same time, but when layered compounds are added, necking occurs but the layered It was found that Ny tends not to decrease due to the interaction between the compound and the polyamide resin molecule. This is because the molecular chains of the film before stretching are randomly oriented in the MD and TD directions, so when the molecular chains are stretched in the MD direction by MD stretching, force in the TD direction is also generated, but normal polyamide In the stretching of the resin, the force applied in the TD direction can be released by necking in the TD direction. On the other hand, in the case of the polyamide resin containing the layered compound, the molecular chain is constrained by the layered compound. Because the force in the direction cannot be released and the molecular chain is stretched in the TD direction as well, or the layered compound rotates during MD stretching. It was thought that the molecule was pulled in the direction of. That is, the plane orientation is already high after uniaxial stretching. For this reason, it was considered that the stretching stress at the time of subsequent TD stretching was increased and the fracture occurred.

  As a method for solving this, by adopting a stretching condition in which Ny decreases after MD stretching, TD stretching performed subsequently can be stretched at a high magnification without causing breakage, etc. It became possible to manufacture on a scale.

  Ny (A) -Ny (B) is preferably 0.001 or more when the refractive index in the width direction before longitudinal stretching is Ny (A) and the refractive index in the width direction after longitudinal stretching is Ny (B). . Further, it is preferably 0.002 or more, most preferably 0.003 or more.

  As a method of lowering Ny after uniaxial stretching, a method of greatly reducing the MD stretching speed can be applied, but the same effect can be obtained by multilayering the unstretched sheet after melt extrusion. Ny can be reduced by reducing the molecular chain entanglement density in the thickness direction by multilayering, thereby improving the ease of deformation of the molecular chain, and as a result, the plane orientation during MD stretching Can be suppressed and TD stretchability can be improved. It has been found that these methods can improve the biaxial stretchability, and can realize a stretched film that is industrially highly practical and excellent in properties.

(Structure of the film)
The biaxially stretched multilayer polyamide resin film of the present invention is obtained by stretching an unstretched polyamide resin multilayer sheet having a total number of 8 layers or more. In the present invention, the number of layers is preferably 8 or more, and more preferably 16 or more. If it is less than 8 layers, the effect of lowering the entanglement density in the thickness direction is small and the effect for reducing boil distortion is small, which is not preferable. The number of layers is preferably 10,000 layers or less, more preferably 5,000 layers. If it exceeds 10,000 layers, the thermal shrinkage after heat setting is not reduced, which is not preferable.

  The thickness of each layer before stretching is preferably in the range of 10 nm to 30 μm, more preferably 100 nm to 10 μm. If it is less than 10 nm, the heat shrinkage rate after heat setting is not small, which is not preferable. On the other hand, if it exceeds 30 μm, the effect of lowering the entanglement density in the thickness direction is small, and the effect for improving the stretchability is small.

(Lamination method)
In the present invention, when the above-described polyamide resin is multilayered, it is possible to laminate the same kind of resin in addition to the lamination of different kinds of commonly employed resins. Here, it may be difficult at first glance to find out the physical meaning of multilayering the same kind of resin by the method described later, but in an actual system, the same kind of resin was melt-extruded and laminated at the same temperature. In some cases, the interface of the layers does not disappear and exists even after stretching. This is synonymous with the fact that it is very difficult to eliminate the weld line of the injection molded product. Thus, even if it is the same kind of resin, a multilayer state is maintained, and it is possible to maintain low molecular entanglement in the thickness direction. As a method of confirming the existence of the interface of layers when melt-extrusion and lamination of the same kind of resin, after cooling the sample with ice or liquid nitrogen, cutting out with a razor or the like, creating a cross section, and then immersing it in a solvent such as acetone It can be observed by a method of observing the cross section with a microscope.

  Polyamide resin and, if necessary, the resin composition constituting the other layers are supplied to separate extruders and extruded at a temperature equal to or higher than the melting temperature, but the melting temperature is 5 ° C. lower than the decomposition start temperature or lower. It is preferable that Also, when using a resin containing a layered compound, the melting conditions and the melting temperature should be set carefully in order to suppress cracking of the layered compound in the resin. For example, in the case of a high molecular weight polyamide resin If the melting is performed at a low temperature such as a melting point of less than + 10 ° C., the layered compound is cracked, the aspect ratio becomes smaller than the initial state, and the effect of using the layered compound having a high aspect ratio is reduced. It is preferable to melt at a high temperature within a range where there is no problem in terms of stability.

  The polyamide resin and, if necessary, the resin composition constituting the other layer are laminated by various methods, and methods such as a feed block method and a multi-manifold method can be used. In the case of the feed block method, when the width is expanded to the die width after lamination, if there is a large difference in melt viscosity between the layers to be laminated or a temperature difference during lamination, lamination unevenness will occur, resulting in deterioration in appearance and thickness unevenness. Therefore, it is preferable to pay attention during the production. In order to suppress unevenness, etc., the melt viscosity at the time of extrusion is adjusted by (1) lowering the temperature, (2) adding various additives such as polyfunctional epoxy compounds, isocyanate compounds, carbodiimide compounds, etc. Preferably it is done.

  In the present invention, the in-plane orientation of the layered compound is promoted by the shearing force at the time of lamination, whereas the stress concentration at the time of stretching is concentrated at the tip of the layered compound, making it difficult to break. As a suitable method for such purpose, lamination by a feed block method or a static mixer method is preferable.

The difference in melting temperature of each layer when the polyamide resin is laminated is 70 ° C. or less, preferably 50 ° C. or less, more preferably 30 ° C. or less. In addition, the difference in melt viscosity of the resin between the layers is within 30 times, preferably within 20 times, more preferably within 10 times the estimated shear rate in the die, thereby suppressing the appearance and unevenness during lamination. It becomes possible. In adjusting the melt viscosity, the addition of the aforementioned polyfunctional compound can be used. The static mixer temperature or feed block temperature at the time of lamination is 150 to 330 ° C, preferably 170 to 220 ° C, more preferably 180 to 300 ° C. A higher viscosity during laminating results in a better laminating state, so a lower feedblock temperature or static mixer temperature is preferable, but if the feedblock temperature or static mixer temperature is too low, the melt viscosity becomes too high and the extruder is fed. This is not preferable because the load on the surface becomes too large. When the temperature is high, the viscosity is too low and uneven lamination occurs, which is not preferable.

  Multi-manifold stacking is also possible, and the above-mentioned problem of uneven stacking is unlikely to occur. However, when laminating layers with different melt viscosities, poor wraparound of each layer resin occurs at the end. In this case, it is preferable to control the difference in melt viscosity.

  The die temperature is the same as described above, but is preferably in the range of 150 to 300 ° C, preferably 170 to 290 ° C, more preferably 180 to 285 ° C. If the temperature is too low, the melt viscosity becomes too high and the surface becomes rough and the appearance deteriorates. An excessively high temperature is not preferable because, besides the thermal decomposition of the resin, the difference in melt viscosity becomes large and unevenness occurs as described above, and particularly unevenness with a small pitch occurs.

(Stretching method)
The biaxially stretched polyamide resin film of the present invention can be stretched by sequential biaxial stretching and simultaneous biaxial stretching of an unstretched sheet melt-extruded from a T die, and a method such as a tubular method can be used, but sufficient orientation In order to perform this, a method using a biaxial stretching machine is preferable. A preferable method from the standpoints of characteristics and economy includes a method of stretching in the longitudinal direction with a roll type stretching machine and then stretching in the transverse direction with a tenter type stretching machine (sequential biaxial stretching method). As for MD stretching, it is preferable to use MD multistage stretching because it is preferable to reduce the MD orientation during MD stretching in order to reduce bowing.

  A substantially unoriented polyamide resin sheet obtained by melt extrusion from a T-die is stretched 2.5 to 10 times in the longitudinal direction at a glass transition temperature Tg ° C. or higher and 150 ° C. or lower of the polyamide resin, and further obtained. It is preferable that the longitudinally stretched film is stretched 3.0 to 10 times at a temperature of 50 ° C. or more and 155 ° C. or less, and then the biaxially stretched polyamide resin film is heat-set at a temperature range of 150 to 250 ° C. .

  The temperature rising crystallization temperature can be determined by heating the sample that has been rapidly cooled after melting the resin by DSC.

  In MD stretching, when the temperature of the film is lower than the glass transition temperature Tg ° C. of polyamide, problems of breakage and thickness unevenness due to orientation crystallization due to stretching occur. On the other hand, when the temperature of the film exceeds 150 ° C., breakage occurs due to crystallization by heat, which is inappropriate. Further, the MD draw ratio in the present invention is preferably 2.5 to 5.0 times, and more preferably 2.8 to 4.5 times. If the draw ratio in MD drawing is less than 2.5 times, problems such as poor quality such as thickness unevenness and insufficient strength in the longitudinal direction occur, and if it exceeds 5 times, the effect of reducing the boil distortion is unfavorable. The MD stretching may be performed in a single stage or in multiple stages.

  Furthermore, when the temperature of the film in TD stretching is a low temperature of less than 50 ° C., the TD stretchability is poor and breakage occurs, and the thickness variation in the TD direction due to neck stretching increases, which is not preferable. When the temperature is higher than 150 ° C., thickness spots increase, which is not preferable. In the present invention, the TD draw ratio is preferably 3.0 to 6.0 times. If it is less than 3.0 times, the maximum point stress under low humidity of MD becomes small, which is not preferable, and the plane orientation becomes low, so that the puncture strength and pinhole resistance are deteriorated. On the other hand, if the TD stretch ratio exceeds 6.0 times, the change in characteristics under low humidity and high humidity is unfavorable. A more preferable TD stretch ratio is 3.0 to 5.0 times.

  When the biaxially stretched multilayer polyamide resin film of the present invention is produced, the draw ratio in terms of area is preferably in the range of 6 to 25 times, more preferably in the range of 9 to 22 times. If it is less than 6 times, sufficient plane orientation is not obtained, and mechanical properties and the like are deteriorated. On the other hand, if it exceeds 25 times, the shrinkage stress increases and the boil distortion deteriorates, which is not preferable.

  The stretching temperature is sufficient to exhibit the effect of adding the layered silicate, and stretching at a low temperature is preferred in terms of film thickness unevenness, gelboflex resistance and the like. Preferable conditions include stretching so that the film temperature is 155 ° C. or lower during TD stretching.

(Heat fixing)
When the heat setting temperature is lower than 150 ° C., the effect of heat setting by the heat of the film is small and inappropriate. On the other hand, a high temperature exceeding 250 ° C. is inappropriate because it causes poor appearance due to whitening caused by thermal crystallization of polyamide and a decrease in mechanical strength.

  In a system containing a layered compound, an increase in density due to crystallization and volume shrinkage associated therewith occur in heat setting after TD stretching, but in the case of a resin containing a layered compound, the generated stress is very large, Rapid heating causes stress in the MD direction and breaks. For this reason, as a heating method at the time of heat setting, it is preferable to increase the amount of heat in a stepwise manner to suppress the generation of a rapid contraction stress. As a specific method, there are methods such as gradually increasing the temperature or increasing the air volume from the vicinity of the entrance of the heat setting zone to the vicinity of the exit, and gradually reducing the air volume in terms of the heat shrinkage rate after stretching and heat setting. The heat setting method which raises is preferable.

  Regarding the relaxation treatment, it is preferable to determine the relaxation rate in consideration of the balance with the thermal contraction rate in the vertical direction. In the present invention, since the longitudinal dimension change in moisture absorption is small, the relaxation rate is preferably in the range of 0 to 5%. If it exceeds 5%, the effect for reducing the thermal shrinkage in the width direction is small, which is not preferable.

(Equilibrium water absorption)
The equilibrium water absorption of the biaxially stretched multilayer polyamide resin film in the present invention is preferably in the range of 3.0 to 7.0%. The equilibrium water absorption is higher than that of the polyamide resin film not containing the layer compound, but this is because the layer compound has high water absorption. Equilibrium water absorption varies depending on the amount of layered compound added, but also varies depending on the stretching conditions, and tends to decrease with increasing plane orientation, so the final film equilibrium water absorption depends on the amount of layered compound added. Determined by stretching conditions. If the equilibrium water absorption is less than 3.0%, the elongation under high humidity is not preferable. On the other hand, if the equilibrium water absorption exceeds 7%, water is volatilized during drying and a problem due to water absorption occurs during processing, which is not preferable.

(Maximum point stress, elongation)
The biaxially stretched multilayer polyamide resin film in the present invention is stored for 12 hours at a humidity of 40% determined by the method described in JIS K 7113 under conditions of an original length of 40 mm, a width of 10 mm and a deformation rate of 200 mm / min stored at a relative humidity of 40%. The ratio of the product (X1) of the maximum point stress (MPa) and the elongation at break (%) of the stored sample to the product (X2) at a relative humidity of 80% is preferably in the range of 1.0 to 1.5.
The toughness of the film is determined by calculating the area under the stress-strain curve. Normal nylon film is a highly ductile film with high elongation and maximum point stress under high humidity, while it has low maximum point stress and elongation at low humidity. It is impossible in practice to design mechanical properties.
On the other hand, a film in which the layered compound is oriented in the plane has the effect of increasing the maximum point stress under low humidity without changing the characteristics under high humidity as compared with a normal nylon film. And found the present invention. The reason for this is that it contains a highly hygroscopic material to provide mechanical reinforcement under low humidity, and under high humidity, due to its hygroscopicity, it imparts moderate molecular chain mobility to reduce elongation, etc. It is estimated that it is possible to suppress this.

  Polyethylene terephthalate is an example of a film that is not affected by humidity. In this case, the ratio is approximately 1.0. By approaching 1.0, it can be said that the film has low humidity dependency with respect to the above characteristics. When the ratio exceeds 1.5, a film having high humidity dependency such as a normal nylon film is formed, which is not suitable for the purpose of the present invention. In order to bring the ratio close to 1.0, the stretching conditions described above, particularly the stretching ratio in the MD direction and the stretching ratio in the TD direction are important.

  Specifically, the MD draw ratio is preferably 2.5 to 5.0 times, and more preferably 2.8 to 4.5 times. MD stretching may be single-stage or multi-stage. When the MD magnification is less than 2.8 times, the plane orientation after biaxial stretching is not improved, and the mechanical properties at low humidity are lowered, which is not preferable. On the other hand, if it exceeds 5 times, not only the characteristics such as boil distortion will be lowered, but also the stability during stretching will be lowered. The TD stretch ratio is preferably 3.0 to 6.0 times. If it is less than 3.0 times, the maximum point stress under low humidity of MD becomes small, which is not preferable, and plane orientation becomes low. On the other hand, if the TD stretch ratio exceeds 6.0 times, the change in characteristics under low humidity and high humidity is unfavorable. A more preferable TD stretch ratio is 3.0 to 5.0 times. In the present invention, the draw ratio in terms of area is preferably in the range of 6 to 25 times, more preferably in the range of 9 to 22 times. If it is less than 6 times, sufficient plane orientation is not obtained, and mechanical properties and the like are deteriorated. On the other hand, if it exceeds 25 times, the shrinkage stress increases and the boil distortion worsens.

(Film characteristics-haze)
The haze of the polyamide resin film in the present invention is preferably in the range of 1.0 to 20%. If the haze at the time of stretching is less than 1.0%, it is difficult to produce stably, which is not preferable. If the haze exceeds 20%, it is not preferable because the design properties are deteriorated in addition to making it difficult to see the contents during use.

  The haze in the system containing the layered compound of the present invention is the sum derived from the resin, the layered inorganic compound, and the void derived from the exfoliation of the resin at the time of stretching on the surface of the layered inorganic compound. It is preferable that the stretching conditions are set carefully. Specifically, when the MD temperature is too low, the haze increases due to the formation of voids, which is not preferable. Also, when the TD temperature is too high, haze increases due to crystallization, which is not preferable. The preferred temperature range is as described above, but can be adjusted with reference to this. Furthermore, it can adjust with the magnitude | size and kind of layered compound. For example, it is possible not only to reduce the haze by using a layered compound that is smaller than the wavelength of visible light, but also to employ a layered compound having a refractive index close to that of the resin. Can reduce the haze.

(Film characteristics-pinhole resistance)
The biaxially stretched film in the present invention is excellent in pinhole resistance, and the number of pinholes after 1000 gelboflex tests at 23 ° C. is preferably 0-30. It is mainly the stretching conditions that have an influence on the resistance to pinholes, and among them, it is preferable that the temperature during TD stretching is not particularly high. If the TD stretchability is poor, the temperature may be raised, but if the stretching temperature is raised too much above the low temperature crystallization temperature, crystallization proceeds partially without sufficient stretching, resulting in a thickness in a fine region. Unevenness and pinholes are likely to occur. Also, pinholes are likely to occur in the obtained film.

  Specifically, the TD stretching temperature is preferably lower than 155 ° C. If it exceeds 155 ° C., the film becomes fragile and the pinhole resistance deteriorates, which is not preferable.

(Film characteristics-equilibrium water absorption)
The biaxially stretched polyamide resin film in the present invention preferably has an equilibrium water absorption in the range of 3.0 to 7.0%. The equilibrium water absorption of a general polyamide resin biaxially stretched film is about 3%. The film of the present invention is preferably higher than that. Of the generally known layered compounds, montmorillonite and smectite, which are most commonly used, are generally used as thickeners for increasing the viscosity of aqueous solutions. As can be imagined from this, water is taken in between the layers, easily swells, and absorbs a large amount of water. If only these compounds are added to the resin, the montmorillonite absorbs a large amount of water. Therefore, the equilibrium water absorption of the resin composition is a large value, and the characteristics are also highly dependent on humidity. According to the present invention, the layered compound is highly oriented in the plane, and the equilibrium moisture content is 3.0% or more by subjecting the polyamide resin of the matrix to biaxial stretching at a high magnification and further orientational crystallization. Even with such an added amount, the humidity dependency of the characteristics can be kept low. If the equilibrium water absorption is less than 3.0%, the effect of the addition of the layered compound is small, and if it exceeds 7%, the humidity dependence is unfavorably large.

(Film characteristics-gas barrier properties)
In the present invention, the multilayer film containing a layered compound has excellent barrier properties because the layered compound is oriented in the plane, and the oxygen permeability in terms of 15 μm is 5 to 20 cc / m ² / day / atm. It is preferable that it exists in the range. The upper limit of the oxygen permeability is preferably at most ^{19cc / m 2 / day / atm} , more preferably not more than ^{18cc / m 2 / day / atm} . The oxygen barrier property depends on the in-plane orientation degree and addition amount of the layered compound in the polyamide resin, and the preferred layered compound addition amount from the viewpoint of the oxygen barrier property is within a range of 0.3 to 20% with respect to the entire film. Yes. If it is less than 0.3%, the barrier effect is small, and if it exceeds 20%, the barrier effect is saturated.

(Film characteristics-thermal shrinkage)
The biaxially stretched multilayer polyamide resin film in the present invention preferably has a heat shrinkage rate at 160 ° C. for 10 minutes in the range of −3.0 to + 3.0% in both the longitudinal direction and the transverse direction. In order to bring the thermal shrinkage rate close to zero, it is preferable to optimize the layer thickness in addition to optimizing stretching conditions and heat setting conditions. It is advantageous to reduce the thickness of each layer in order to improve stretching stress reduction. However, if the layer becomes too thin, the heat shrinkage rate cannot be reduced due to heat fixation, etc., and the layer structure matches the desired heat shrinkage rate. However, in order to achieve both heat shrinkage and stretchability, the thickness of each layer before stretching is more preferably in the range of 1 to 30 μm, and still more preferably in the range of 2 to 20 μm. The lower limit value of the heat shrinkage rate is more preferably −1.0% or more, and further preferably 0.1% or more. The upper limit is preferably + 3.0% or less, and more preferably 1.3% or less.

(Film characteristics)
The multilayer film in the present invention preferably has a dimensional change in the range of 0.1 to 1.0% in both the vertical and horizontal directions when it is changed from 25 ° C. and a relative humidity of 35% to 25 ° C. and a relative humidity of 85%. The heat shrinkage rate and moisture absorption dimensional change rate in the width direction can be adjusted slightly depending on the relaxation rate in the width direction during heat setting, but it is an essential problem in the longitudinal direction, especially in sequential biaxial stretching. It is very difficult to reduce the hygroscopic dimensional change rate in view of balancing with other characteristics. Conventional polyamide resins have been pointed out that hydrogen bonds due to amide groups between molecular chains are easily broken by water and cause dimensional changes. Polyamide resins in which layered compounds are uniformly dispersed are not compatible with layered compounds and molecular chains. It is estimated that it is possible to suppress the change in moisture absorption dimensionality by using these, and it is possible to suppress the change in moisture absorption dimension by using these. Because it was not, realization was not achieved. By stretching the sheet having a multilayer structure in the present invention, it is possible to impart high dimensional stability during moisture absorption.

  The multilayer film in the present invention preferably has a heat shrinkage rate at 160 ° C. for 10 minutes in the range of −3 to 3% in both the vertical and horizontal directions. In order to bring the thermal shrinkage rate close to zero, it is preferable to optimize the layer thickness in addition to optimizing stretching conditions and heat setting conditions. Although it is advantageous to reduce the thickness of each layer in order to improve stretchability, the reason is unclear, but the present inventors have found that if the layer becomes too thin, the heat shrinkage rate cannot be reduced by heat fixation or the like. I found it. For this reason, it is preferable to determine the layer structure in accordance with the target heat shrinkage rate, and in order to achieve both heat shrinkage rate and stretchability, the thickness of each layer before stretching is more preferably within the range of 1 to 30 μm. More preferably, it is in the range of 2 to 20 μm. The lower limit value of the heat shrinkage rate is more preferably 0% or more, and further preferably 0.1% or more. The upper limit is preferably 3.0% or less, and more preferably 2.5% or less.

  The biaxially stretched polyamide resin film of the present invention may be subjected to corona treatment, coating treatment or flame treatment in order to improve adhesion and wettability depending on the application. In the coating process, an in-line coating method in which a film coated during film formation is stretched is one preferred embodiment. In general, the biaxially stretched polyamide resin film of the present invention is further subjected to processing such as printing, vapor deposition, and lamination depending on the application.

  The biaxially stretched polyamide resin film of the present invention has a hydrolysis resistance improver, antioxidant, colorant (pigment, dye), antistatic agent, conductive agent, flame retardant, reinforcing agent, filler, inorganic lubricant, organic A lubricant, a nucleating agent, a mold release agent, a plasticizer, an adhesion assistant, a pressure-sensitive adhesive, and the like can be optionally contained.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not restrict | limited at all to these examples, unless the summary is exceeded. The measurement method used in the present invention is shown below.

(1) Haze
The sample was measured at three different locations using a haze meter (Nippon Denshoku, NDH2000) by a method according to JISK7105, and the average value was defined as haze.

(2) Glass transition temperature (Tg) measurement and low-temperature crystallization temperature (Tc) measurement An unoriented polyamide resin sheet is frozen in liquid nitrogen, decompressed and thawed, using a DSC manufactured by Seiko Denshi Co., Ltd. Measured with

(3) Addition amount of inorganic substance including layered compound (weight residue)
Using TA Instruments TGA, the weight residue was obtained after heating up to a sample amount of 0.1 g, a nitrogen stream and a temperature increase rate of 20 ° C./min to 500 ° C.

(4) Plane orientation The plane orientation was determined by the following formula using an Abbe refractometer.

ΔP = (Nx + Ny) / 2-Nz

Here, Nx represents the refractive index in the longitudinal direction, Ny represents the refractive index in the width direction, and Nz represents the refractive index in the thickness direction.

(5) Mechanical properties (maximum point stress, elongation at break)
Conforms to JIS K 7113. A sample having a width of 10 mm and a length of 100 mm in the longitudinal direction and the width direction of the film was cut out using a razor as a sample. After being left for 12 hours in an atmosphere of 23 ° C and 35% RH, the measurement was performed in an atmosphere of 23 ° C and 35% RH under the conditions of a distance between chucks of 40 mm and a pulling speed of 200 mm / min. Values were used. As a measuring device, an autograph AG5000A manufactured by Shimadzu Corporation was used.

(6) Relative viscosity 96% sulfuric acid solution 0.25 g of nylon resin was dissolved in 25 ml, and the relative viscosity was measured at 20 ° C.

(7) Observation of orientation state of layered compound in film A sample was prepared by the following method and observed using a transmission electron microscope. First, the sample film was embedded in an epoxy resin. As the epoxy resin, a mixture of Luavec 812, Luavec NMA (manufactured by Nacalai Tesque) and DMP30 (TAAB) in a weight ratio of 100: 89: 3 was used. After embedding the sample film in an epoxy resin, the sample film was left in an oven adjusted to a temperature of 60 ° C. for 16 hours to cure the epoxy resin and obtain an embedded block.

The obtained embedding block was attached to an ultra cut N manufactured by Nissan Sangyo, and an ultrathin section was prepared. First, trimming was performed using a glass knife until a cross section of a portion desired to be observed for the film appeared on the resin surface. Next, an ultrathin section was cut out using a diamond knife (Sumitomo Electric, Sumiknife SK2045). After cutting out the ultrathin section on the mesh, carbon deposition was performed thinly.
The electron microscope observation was carried out using JEM-2010 manufactured by JEOL under the condition of an acceleration voltage of 200 kV. An image obtained by electron microscopic photography of the film cross-section was recorded on an imaging plate (FDLUR-V, manufactured by Fuji Photo Film). From the images, 50 layered compounds were randomly extracted and the inclination of each was evaluated. When the variation in the inclination of any layered compound falls within an angle of 20 degrees or less, the in-plane orientation is indicated by ◯, and otherwise it is indicated by ×.

(8) Layer thickness and total number of layers in the film The film was cooled with liquid nitrogen and taken out immediately, and cut out in the width direction of the cast film with a feather blade to obtain a cross section. This cross section was observed using an optical microscope (Olympus BX60), and a value obtained by dividing the thickness of the layer for 5 to 20 layers by the number of layers was determined as the layer thickness. The total number of layers was determined by the same method.
When it was difficult to understand the interface of the layer by the above method, a sample was prepared by the following method and observed using a transmission electron microscope. First, the sample film was embedded in an epoxy resin. As the epoxy resin, a mixture of Luavec 812, Luavec NMA (manufactured by Nacalai Tesque) and DMP30 (TAAB) in a weight ratio of 100: 89: 3 was used. After embedding the sample film in an epoxy resin, the sample film was left in an oven adjusted to a temperature of 60 ° C. for 16 hours to cure the epoxy resin and obtain an embedded block.
The obtained embedding block was attached to an ultra cut N manufactured by Nissan Sangyo, and an ultrathin section was prepared. First, trimming was performed using a glass knife until a cross section of a portion desired to be observed for the film appeared on the resin surface. Next, an ultrathin section was cut out using a diamond knife (Sumitomo Electric, Sumiknife SK2045). After cutting out the ultrathin section on the mesh, carbon deposition was performed thinly.
The electron microscope observation was carried out under the condition of an acceleration voltage of 200 kV using JEM-2010 manufactured by JEOL. An image obtained by electron microscopic photography of the film cross-section was recorded on an imaging plate (FDLUR-V, manufactured by Fuji Photo Film). From the image, the thickness of the layer having the maximum thickness was measured from the distance between the interfaces of each layer.

(9) Equilibrium water absorption
A 10 cm square sample was dried under vacuum at 60 ° C. for 24 hours, and its weight (a) was measured. Then, it was left for 12 hours in an environment of 40 ° C. and 90% RH, and the weight (b) was measured. The equilibrium water absorption was determined by the following formula.

Equilibrium water absorption (%) = (ba) / a × 100

Example 1
Nylon 6 resin pellets with montmorillonite uniformly dispersed as a layered compound (NF3040 from Nanopolymer Composite Corp., layered compound addition amount: 4%) are vacuum-dried at 100 ° C overnight, then the same for two extruders , Melted at 280 ° C, laminated using a 16-element static mixer heated to 280 ° C, extruded from a T-die heated to 275 ° C in a sheet form on a cooling roll adjusted to 20 ° C, cooled and solidified By doing so, a multilayer unstretched sheet was produced. The ratio of the discharge amount of the two extruders was 1: 1. The unstretched sheet had a thickness of 180 μm, the thickness of each layer from the cross section was about 1 μm, and the number of layers was 100 or more. The sheet had a Tg of 35 ° C. and a melting point of 225 ° C. This sheet is first preheated at a temperature of 45 ° C., then stretched longitudinally by 3.2 times at a stretching temperature of 85 ° C. at a deformation rate of 4500% / min, and this sheet is continuously guided to a tenter, with a preheating temperature of 110 ℃, stretched 3.8 times at a stretching temperature of 130 ℃, heat-fixed at 210 ℃ and subjected to 5% transverse relaxation treatment, cooled, cut and removed the unstretched portion in the width direction, A biaxially stretched polyamide resin film was obtained. The film had a width of 40 cm and a length of 1000 m and was wound around a paper tube. Table 1 shows the film physical properties at this time.

(Examples 2-3, Comparative Examples 2-4)
Samples were prepared in the same manner as in Example 1 under the conditions described in Table 1. Table 1 shows the film characteristics and the like. In Example 3, a multilayer sheet was prepared using a 6-element static mixer, and in Comparative Example 4, a sample was prepared using a single layer sheet using a feed block having a single layer structure.

(Comparative Example 1)
Nylon 6 resin pellets (NF3040 manufactured by Nanopolymer Composite Corp., layered compound addition amount: 4%) in which montmorillonite was uniformly dispersed as a layered compound were vacuum-dried at 100 ° C. overnight. Next, it formed into a film using the single layer inflation film forming machine. The pellets were fed into an extruder and melted at 290 ° C. Subsequently, it was extruded from an annular die heated to 280 ° C., and while being air-cooled, it was adjusted so as to obtain a draw ratio of 4 times in terms of area from the discharge amount, winding speed, and tube diameter. The center part of the tube was cut to obtain a biaxially stretched polyamide resin film having a thickness of 15 μm. The film had a width of 40 cm and a length of 1000 m and was wound around a paper tube. Table 1 shows the film physical properties at this time.

  Since the conventional polyamide resin film has mechanical properties that change depending on the humidity, it is necessary to perform humidity control when processing such as printing, and to perform processing under conditions that take into account changes in properties in advance. By stretching a multilayer polyamide resin containing a layered compound under specific conditions, a mechanical property at low humidity can be improved, and a film with reduced humidity dependence of impact strength at low speed can be produced with high productivity.

Claims (1)

  A biaxially stretched polyamide resin film obtained by adding 0.3 to 20% by weight of an inorganic substance containing a layered compound, laminated in 8 or more layers, and stretched 2.5 to 5.0 times in the longitudinal direction and 3.0 to 6.0 times in the width direction. 12 hours at a humidity of 40% required by the method described in JIS K 7113 under the conditions of an equilibrium water absorption of 3.0 to 7.0% and an original length of 40 mm, a width of 10 mm and a deformation rate of 200 mm / min stored at a relative humidity of 40%. The product of the maximum point stress (MPa) and the breaking elongation (%) of the stored sample (X1), and the maximum point stress (MPa) and the breaking elongation (%) of the sample stored for 12 hours at 80% relative humidity A biaxially stretched polyamide resin film, wherein the product (X2) ratio is in the range of 1.0 to 1.5.